I understand that usually the Xgrid is used for huge math/scientific calculations. Can it be used for other purposes like video/3D rendering or photoshop.. with a small setup of, for instance, 3 or 4 minis? Does Xgrid needs special software/programs?

Xgrid could be used for video/3D rendering, but the software would have to be written specifically for this, you can't just set up an Xgrid and have word and excel running twice as fast!

One good current use for a mini might be as a Logic node for audio processing. I think the software for each node is free, so you'd only be paying for the hardware. Unfortunately though gigabit ethernet is going to make a big difference in that sort of application, which the mini doesn't have, though you could use a firewire network._________________Mac Mini Predictions